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More on Doping Speakers

Posted 25th May 2013 at 10:25 AM by googlyone

I got a question or two on doping of speaker surrounds.

Here is the thing: If you buy an OEM cone kit it will either come with a pre-doped surround, or be provided with the doping material and instructions.

I have reconed a lot of drivers and until recently either used OEM kits or kits from providers who have looked after this for me.

A good example of a provider that gave doping compound was BEYMA. The instructions etc for this were idiot proof, and the material nicely packed in the kit.

To apply this I used a stiff "cleaning brush" as you would but from your local hardware store - a steel handle about 100mm (4") long crimped onto stiff bristles. Worked a treat.

The beyma doping material looked and smelt for the world like really thick PVA glue. The difference was that when dry it did not go that hard, and remained almost but not quite tacky.

The before shot is:
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Old

Doping of cloth surrounds on recone of subwoofer

Posted 14th May 2013 at 12:32 PM by googlyone

Well, you learn something every day. I suppose if you don't manage to learn as you go, then you probably stuff things up every day!!!

About 12 months ago I came across some RCF L18/551 eighteen inch subwoofer baskets. I reconed them using aftermarket parts, the process went OK but I was kind of bemused by the untreated cloth surrounds.

I was busy, and had no immediate plans so the drivers were shelved for a rainy day.

The Thielie and Small parameters were "OK" but not exact as OEM. I measured these using the addded mass method, an important fact for later. As an aside, they would do well enough as subs, but their Fs was a bit higher than I would have hoped.

Fast forward to last week, I loaded one into a 220 litre box tuned to 34Hz, and measured the impedance.

Bugger me if the resonance showed one massive peak at pretty much the driver Fs, and a tiny lump out at 80Hz. Huh?

I swapped drivers...
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